In medical practice, a medical diagnostic imaging device using a photographic technique has been in wide use. With the medical diagnostic imaging device, a specific portion (e.g., bone or lungs) of a patient is irradiated with X-rays, an X-ray film is exposed to X-rays passing through the specific portion, and the X-ray film is developed to visualize a state inside the specific portion.
Since the method using X-ray films needs a storage space for the X-ray films and maintenance thereof is troublesome, digitization of images is in progress. As a method for digitizing images, a method using an imaging plate containing a material which emits light by being irradiated with X-rays (photostimulable material) has been known. By sensing light emitted from the imaging plate with scanner, digitized images can be obtained.
The imaging plate is a plate to which photostimulable phosphor is applied and which has higher sensitivity to X-ray absorption difference than X-ray films. Data of X-ray irradiation can be erased, so that the imaging plate can be re-used. However, data obtained by the imaging plate is analog, which requires treatment for digitization to digitize the data.
For this reason, attention has been recently focused on flat panel detectors capable of obtaining digital data directly (e.g., Patent Document 1). Flat panel detectors have two systems, direct and indirect conversion systems. In the direct conversion system, X-rays are directly converted to electrical charges with the use of an X-ray detecting element. In the indirect conversion system, X-rays are converted to visible light with a scintillator and the light is converted to electrical charges by a photodiode. In either of the systems, a flat panel detector includes a plurality of pixel circuits arranged in a matrix.